The use of grain legumes as a protein source in pig nutrition: A review

Grain legumes are valuable sources of protein and energy for monogastric animals. Grain legumes, such as faba beans, peas and lupins, can partially or even totally replace traditional protein sources of animal origin such as meat and bone meal or fish meal. Moreover, they represent an alternative protein-rich feed ingredient for soybean meal (SBM) and other oilseed meals. However, the presence of secondary plant metabolites, also referred to as antinutritional factors, such as protease inhibitors, saponins, pyrimidine glycosides, lectins, tannins, and alkaloids, has restricted the use of grain legumes in pig feeding. Furthermore, a high proportion of α-galactosides present in some grain legumes may lead to excessive fermentation and diarrhoea, while high levels of non-starch-polysaccharides (NSP) may have a negative impact on energy utilisation. Among different processing methods designed to further improve the nutritive value through reductions in content of secondary plant metabolites, recent progress in plant breeding has contributed to the commercial release of cultivars with improved feeding value in association with lower contents of secondary plant metabolites. This review focuses on the evaluation of the nutritional value of currently available cultivars of faba beans, peas and lupins, and their use in pig diets. Special interest is directed to nutritional composition, energy and amino acid (AA) digestibility of faba beans, peas and lupins, but also to their contents of secondary plant metabolites, including the threshold levels to be accounted for in diet formulation for pigs. Furthermore, feed processing technologies developed to improve the nutritive value of grain legumes are introduced.